Go about designing a world map for game engines
There is indeed a difference between having one giant soil and placing elements on it and dispatching pieces of landscape where it is needed. Since you have an incline, I suggest the first. I strongly reccomend that you work with armory3d which is the pbr engine for blender. Thus with arrays and displace you can have a soil, add another displace with a texture for the paths/roads, use the nodes with normal -> dot connected to mix shaders via colorramps to get different surfaces types depending on the slope. Even add some tesselation displacement and you'll get quite near to photorealism. The next step is to create/get a grass shader and some vegetation models and dispatch them on that land with a script or grease pencil. That's for the natural part of it.